Data storage device employing differential write data signal and differential write pattern signal

ABSTRACT

A data storage device is disclosed comprising a head actuated over a disk. A first control circuit comprises a pattern detector configured to detect at least one pattern in write data and generate a corresponding multi-state signal, and a transmitter configured to transmit a first differential signal representing the write data and a second differential signal representing the multi-state signal. A second control circuit comprises a receiver configured to receive the first differential signal and the second differential signal, and a write driver configured to generate a write current applied to the head based on the first differential signal and configured to adjust at least one property of the write current based on the second differential signal.

BACKGROUND

Data storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.

Data is typically written to data sectors within a data track by modulating the write current of a write element, for example, using a non-return to zero (NRZ) encoding where a binary “1” is written using positive write current (+1) and a binary “0” is written using a negative write current (−1), thereby writing magnetic transitions onto the disk surface. A read element (e.g., a magnetoresistive (MR) element) is then used to transduce the magnetic transitions into a read signal that is demodulated by a read channel. The recording and reproduction process may be considered a communication channel, wherein communication demodulation techniques may be employed to demodulate the read signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a data storage device according to an embodiment comprising a head actuated over a disk, wherein a first differential signal representing write data is transmitted from a first to second control circuit together with a second differential signal representing a detected pattern in the write data so that the write current applied to the head may be modified accordingly.

FIG. 2A shows control circuitry according to an embodiment comprising a transmitter for transmitting the first and second differential signals and a receiver for receiving the differential signals.

FIG. 2B shows control circuitry according to an embodiment wherein the receiver comprises a decoder for decoding the second differential signal representing the detected pattern in the write data.

FIG. 3 illustrates an embodiment wherein the amplitude and duration of a write current overshoot is adjusted based on the detected pattern in the write data (1T, 2T, 3T, etc.).

DETAILED DESCRIPTION

FIGS. 1A and 1B show a data storage device according to an embodiment comprising a head 2 actuated over a disk 4. A first control circuit 6 comprises a pattern detector configured to detect at least one pattern in write data and generate a corresponding multi-state signal, and a transmitter configured to transmit a first differential signal 10 representing the write data and a second differential signal 12 representing the multi-state signal 8. A second control circuit 14 comprises a receiver configured to receive the first differential signal 10 and the second differential signal 12, and a write driver configured to generate a write current applied to the head 2 based on the first differential signal 10 and configured to adjust at least one property of the write current based on the second differential signal 12.

In the embodiment of FIGS. 1A and 1B, the head 2 is coupled to a distal end of a suspension 16 that is coupled to a distal end of an actuator arm 18. The actuator arm 18 is rotated about a pivot by a voice coil motor (VCM) 20 to move the head 2 radially over the disk 4. In one embodiment, the VCM 20, actuator arm 18, head 2 and disk 4 are enclosed in a housing referred to as a head disk assembly (HDA), wherein the second control circuit 14 (e.g., preamp) is coupled to the actuator arm 18. The first control circuit 6 is adhered to a printed circuit board (PCB) that is mounted to a base of the HDA, wherein the first control circuit 6 is coupled to the second control circuit 14 through a flex circuit (not shown). In order to compensate for various noise sources (e.g., electromagnetic interference), data is transmitted through the flex circuit using differential signals. For example, during a write operation the binary write data at the first control circuit 6 is converted into the first differential signal 10 that is transmitted over the flex circuit to the second control circuit 14 inside the HDA. The second control circuit 14 processes the first differential signal 10 to modulate a write current applied to a write element in the head 2 in order to record a sequence of magnetic transitions on the disk that represents the write data.

In one embodiment, the fidelity of the magnetic transitions recorded on the disk may be affected by properties of the modulated write current. For example, in one embodiment the fidelity of the magnetic transitions and the resulting read-back signal may improve if the amplitude and/or duration of an overshoot in the write current is increased when recording write data having a higher frequency of transitions. Accordingly, in one embodiment the first control circuit 6 in FIG. 1A detects one or more patterns in the write data that requires an adjustment to the write current, and then transmits a corresponding multi-state signal as the second differential signal 12 to the second control circuit 14 together with the write data transmitted as the first differential signal 10. In one embodiment, the first and second differential signals 10 and 12 are transmitted substantially synchronous to one another so that write current may be adjusted by the second control circuit 14 when recording the magnetic transitions representing the detected pattern.

FIG. 2A shows an embodiment wherein the first control circuit 6 comprises a suitable pattern detector 22 configured to detect one or more patterns in the write data 24 and generate a corresponding multi-state signal 26. A transmitter 28 in the first control circuit 6 converts the write data 24 into the first differential signal 10 and converts the multi-state signal 26 into the second differential signal 12. The first and second differential signals 10 and 12 are transmitted (e.g., via a flex circuit) to a suitable receiver 30 in the second control circuit 14. The receiver 30 converts the first differential signal 10 into a write signal 32 applied to a suitable write driver 34 which modulates a write current 36 applied to the write element of the head 2. The receiver 30 also converts the second differential signal 12 into a pattern signal 38 that is decoded by a pattern decoder 40 to generate a control signal 42 applied to the write driver 34 in order to adjust at least one property of the write current (e.g., amplitude and/or duration of an overshoot) based on the detected pattern in the write data 24.

FIG. 2B shows an embodiment of control circuitry within the transmitter 28 and receiver 30 of FIG. 2A for transmitting and converting the second differential signal 12 into the pattern signal 38 representing the pattern detected in the write data. In this embodiment, the multi-state signal 26 is represented as a multi-level voltage, wherein each voltage level represents a detected pattern in the write data. A first differential amplifier 44 within the transmitter 28 amplifies the multi-state signal 26 to generate the second differential signal 12 transmitted to a second differential amplifier 46 within the receiver 30. The second differential amplifier 46 generates the pattern signal 38 having an amplitude that corresponds to a detected pattern in the write data. The pattern signal 38 is compared to different thresholds Th1-ThN at comparators 48 ₁-48 _(N), wherein each threshold Th1-ThN corresponds to a different pattern. The outputs of the comparators 48 ₁-48 _(N) are decoded by a binary decoder 50 into a binary signal 42 applied to the write driver 34. In this embodiment, the binary signal 42 comprises two bits that may represent up to four different patterns in the write data; however, the pattern signal 38 may comprise any suitable number of levels representing any suitable number of patterns, and the binary signal 42 comprising any suitable number of bits needed to represent the number of patterns detected.

FIG. 3 illustrates example patterns for the write data and corresponding waveform for the write current generated to compensate for the detected patterns. In this example, each bit in the write data is recorded on the disk during a bit cell period T. A 1T pattern corresponds to a single bit cell before recording the next magnetic transition, a 2T pattern corresponds to two consecutive bit cells before recording the next magnetic transition, a 3T pattern corresponds to three consecutive bit cells before recording the next magnetic transition, etc. In this example, the binary pattern signal 42 comprises two bits representing three different patterns in the write data (01=1T, 11=2T, 00=greater than 2T). In this embodiment, the second differential signal 12 representing the detected pattern is transmitted to the second control circuit 14 one bit cell in advance of the first differential signal 10 representing the write data so that the write driver 34 may adjust the property of the write current before actually recording the magnetic transition on the disk. In the example of FIG. 3, the amplitude of the overshoot in the write current is increased when recording a 1T pattern, and the amplitude and duration of the overshoot is increased when recording a 2T pattern. Otherwise, the amplitude and duration of the overshoot may be set to a nominal level when recording a 3T (or greater) pattern.

Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.

In various embodiments, a disk drive may include a magnetic disk drive, an optical disk drive, etc. In addition, while the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.

The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.

While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein. 

What is claimed is:
 1. A data storage device comprising: a disk; a head actuated over the disk; a first control circuit comprising: a pattern detector configured to detect at least one pattern in write data and generate a corresponding multi-state signal; and a transmitter configured to transmit a first differential signal representing the write data and a second differential signal representing the multi-state signal; and a second control circuit comprising: a receiver configured to receive the first differential signal and the second differential signal; and a write driver configured to generate a write current applied to the head based on the first differential signal and configured to adjust at least one property of the write current based on the second differential signal.
 2. The data storage device as recited in claim 1, wherein the pattern detector is configured to detect at least three different patterns in the write data and generate the corresponding multi-state signal to represent each detected pattern.
 3. The data storage device as recited in claim 2, wherein the three different patterns comprise a 0T pattern, a 1T pattern, and a 2T pattern.
 4. The data storage device as recited in claim 1, wherein the at least one property of the write current comprises an amplitude of the write current.
 5. The data storage device as recited in claim 1, wherein the at least one property of the write current comprises an overshoot duration of the write current.
 6. The data storage device as recited in claim 1, wherein the first control circuit is configured to transmit the second differential signal substantially synchronous with the first differential signal.
 7. The data storage device as recited in claim 1, wherein the second control circuit further comprises a decoder configured to decode the second differential signal.
 8. A method of operating a data storage device, the method comprising: detecting at least one pattern in write data and generating a corresponding multi-state signal; transmitting a first differential signal representing the write data and a second differential signal representing the multi-state signal; receiving the first differential signal and the second differential signal; and generating a write current applied to a head actuated over a disk based on the first differential signal and adjusting at least one property of the write current based on the second differential signal.
 9. The method as recited in claim 8, wherein detecting at least one pattern comprises detecting at least three different patterns in the write data and generating the corresponding multi-state signal to represent each detected pattern.
 10. The method as recited in claim 9, wherein the three different patterns comprise a 0T pattern, a 1T pattern, and a 2T pattern.
 11. The method as recited in claim 8, wherein the at least one property of the write current comprises an amplitude of the write current.
 12. The method as recited in claim 8, wherein the at least one property of the write current comprises an overshoot duration of the write current.
 13. The method as recited in claim 8, further comprising transmitting the second differential signal substantially synchronous with the first differential signal.
 14. The method as recited in claim 8, further comprising decoding the second differential signal. 